1. Field of the Invention
This invention relates to novel derivatives of tricyclic antidepressant drugs. The derivatives pertain to immunoassays for determining tricyclic antidepressant drugs in liquid media such as biological fluids and include immunogens used to stimulate production of antibodies to the drugs in host animals by conventional techniques. Also provided are labeled conjugates used as reagents, along with the antibodies, in particularly preferred immunoassays. Intermediates in the synthesis of the aforementioned immunogens and labeled conjugates are also provided.
The tricyclic antidepressants are a recognized class of structurally related drugs used for the treatment of depression [The Pharmacological Basis of Therapeutics, 5th ed., ed. Goodman and Gilman, MacMillan Publ. Co. (New York 1975) pp. 174 et seq]. All of the drugs have an annealated three ring nucleus, a "tricyclic" nucleus, which is often, but by no means exclusively, dibenzazepinyl, dibenzocycloheptadienyl, dibenzoxepinyl, or phenothiazinyl in nature. A further common feature found in this class of compounds is the presence of a side chain of substantial length off one of the atoms, usually carbon or nitrogen, in the central ring of the tricylic nucleus. The most commonly administered drugs of this class are imipramine, desipramine, amitriptyline, nortriptyline, protriptyline, doxepin, and desmethyldoxepin.
Because of large individual variation in steady state concentrations of tricyclic antidepressants in patients receiving the same therapeutic dose and a correlation between blood levels and clinical response, it is desirable to monitor the concentration of the drugs in the blood of patients under treatment for depression [Kaul et al, J. Anal. Toxicol. 1: 236-243 (1977)]. Immunoassay is a useful analytical technique for measuring the concentrations of substances (analytes) appearing in biological fluids in the range in which the tricyclic antidepressants appear in blood. In order to establish an immunoassay for a particular analyte it is necessary to synthesize appropriate derivatives of the drug in order to obtain immunogens by which to stimulate specific antibody production and labeled conjugates by which to monitor the immunoassay reaction.
2. Description of the Prior Art
The determination of tricyclic antidepressants by immunoassay is known [Kaul et al, supra]. Homogeneous immunoassays for determining various analytes including drugs are described in U.S. Pat. Nos. 4,279,992; 4,238,565; and 3,817,837 and in British Pat. No. 1,552,607.
Immunogen conjugates, comprising tricyclic antidepressants coupled to conventional immunogenic carrier materials, useful in stimulating the production of antibodies to the drug in animals are described in the literature. Conjugation of side arm derivatives are described in Brunswick et al, Br. J. Clin. Lab. Invest. 40: 191-197 (1980), Aherne et al, Br. J. Clin. Pharm. 3: 561-565 (1976), and U.S. Pat. No. 4,207,307. All of these side arm derivatives involve modification of the drug at the terminal amine group on the side arm. Derivatization off one of the rings is described in Read et al, Postgrad. Med. J. 53(Suppl 4): 110-116(1977), Read et al, Clin. Chem. 24(1): 36-40(1978), and U.S. Pat. Nos. 4,223,013 and 4,275,160. Spector et al, Psychopharm. Commun. 1 (4): 421-429 (1975) describe a desipramine immunogen of undefined structure, although the authors believe that conjugation is off the benzyl ring. Immunogens of the related drug carbamazepine with conjugation off its somewhat shortened side arm are described in U.S. Pat. No. 4,058,511.
The state-of-the-art of preparing antibodies to haptens such as drugs is represented by Weinryb et al, Drug Metabolism Reviews 10: 271(1979); Playfair et al, Br. Med. Bull. 30: 24(1974); Broughton et al, Clin. Chem. 22: 726(1976); and Butler, J. Immunol. Meth. 7: 1(1975) and Pharmacol. Rev. 29(2): 103-163(1978).
Labeled conjugates, comprising the analyte or a derivative or other analog thereof, coupled to a labeling substance are variously described in the literature, e.g., the aforementioned U.S. Pat. No. 4,279,992, wherein the label is the fluorogenic enzyme substrate .beta.-galactosyl-umbelliferone (.beta.GU), and U.S. Pat. No. 4,213,893, wherein the label is flavin adenine dinucleotide (FAD).
Literature pertaining to the derivatization of tricyclic antidepressants and related compounds is referred to in the ensuing text.